1. Field of the Invention
The present invention relates to a process for the metathesis of olefins. More particularly the invention relates to a process including the preparation of purified metathesis feed. More particularly the invention relates to a process wherein the catalyst is part of a distillation structure and the products are simultaneously separated from the reactants and each other by fractional distillation during the reaction.
2. Related Art
Broadly metathesis has been defined as a chemical reaction in which an element or radical in one compound changes places with another element or radical in another compound. See The Van Nostrand Chemist's Dictionary, D. Van Nostrand Company, Inc., 1953, page 463. More specifically olefin metathesis can be defined as the redistribution of alkylidene moieties to give a mixture of olefins. In effect, this reaction takes place via cleavage of the olefin double bond. Generally the reactions of olefinic molecules in the presence of metal-containing catalysts to produce other olefinic molecules are known in the art as “disproportionation”, “dismutation” or “metathesis” reactions.
The metathesis reactions generally are of considerable interest because of the versatility of the reaction and the numerous olefinic hydrocarbons available from petrochemical sources which are suitable for use in the reaction to yield useful products. See, for example, U.S. Pat. No. 4,046,832 (metathesis of propylene with itself to produce n-butene and ethylene); U.S. Pat. No. 3,702,827 (the metathesis of 2-methyl-1-propene and 2-butene to produce 2-methyl-2-butene); U.S. Pat. No. 4,709,115 (simultaneous disproportionation of butene with itself to produce ethylene or propylene and hexene or pentenes and fractional distillation); and U.S. Pat. No. 6,583,329 (concurrent metathesis reaction and separation by fractional distillation to produce: (A) propylene from butene; (B) detergent range olefins from the metathesis of C15 and heavier olefins with C9 and lighter olefins; (C) 2-methyl-2-butene and propylene from the metathesis of 2-butene and isobutylene; and (D) tetramethylethylene from the metathesis of isobutylene with itself and/or the reaction of diisobutylene with ethylene to produce neo hexene).
The metathesis of ethylene with n-butene to produce propylene is disclosed in U.S. Pat. No. 5,026,936. However, the purification of 2-butene prior to the metathesis reaction can be quite difficult. If pure 2-butene is not used, a wide range of byproducts are formed and/or the life the metathesis catalyst is shortened. The metathesis requires that the feed olefins be pretreated to remove contaminants such as dienes, water, sulfur, etc. These contaminants dramatically shorten the life of the catalyst. It is an advantage of the present invention that provides an integrated process for the recovery of high purity 2-butene and the conversion by metathesis with ethylene to propylene. It is a further advantage that an optional step in the integrated process provides purification of sulfur compounds and polyolefins from the 2-butene.